Method and device for converting hydrogen sulfide into elemental sulfur

ABSTRACT

In a process for producing elemental sulfur by combustion of hydrogen sulfide or a hydrogen-sulfide-containing gas, in particular a Claus process, the hydrogen sulfide or the hydrogen-sulfide-containing gas undergoes partial combustion by using a first device in the form of a burner to which usually air is added as an oxidizing agent and which is connected to the combustion chamber. The hydrogen sulfide or the hydrogen-sulfide-containing gas undergoes further combustion by means of a second device in form of at least one nozzle which is also connected to the combustion chamber and through which oxygen or an oxygen containing gas is fed into the combustion chamber, as a result of which the hydrogen sulfide or the hydrogen-sulfide-containing gas is subjected to afterburning and is then fed to a waste-heat boiler and thereafter to one or more reactors.

The invention relates to a process and an apparatus for the conversionof hydrogen sulfide (H₂S) into elemental sulfur (S).

Sulfur is required in many chemical processes either in elemental formor in the form of sulfuric acid. However, sulfur is highly toxic in theform of sulfur dioxide (SO₂) or as hydrogen sulfide. Therefore, thereare maximum permissible emission limit values for the sulfur compounds,which are becoming increasingly more stringent worldwide.

Fossil fuels, such as natural gas, coal, oil sand, oil shale andpetroleum, comprise organic and inorganic sulfur compounds. It isnecessary to remove these sulfur compounds or to convert them intoharmless sulfur compounds. To remove the sulfur compounds from fuels andcombustion products there exists a multiplicity of physical and chemicalconversion processes.

In the case of solid fuels, the sulfur compounds are absorbed after thecombustion in the power station as sulfur dioxide by a flue gasdesulfurization system using milk of lime and converted into calciumsulfite. By oxidation with the residual oxygen present in the exhaustgas, gypsum is formed as end product.

In the case of liquid fuels, such as diesel fuel or light fuel oil,maximum permissible sulfur contents are prescribed. This is because fluegas desulfurization after possible consumption in engines, for example,can no longer be implemented. The desulfurization of these fuels iscarried out in the refineries. The sulfur compounds present in the crudeoil are recovered in the distillate, the heavy oil fraction having thehighest sulfur concentrations.

The desulfurization is performed using gaseous hydrogen (H₂). Theorganic sulfur compounds are converted in this case into hydrogensulfide. The hydrogen sulfide, which is present in the gas mixture withhydrogen and other hydrocarbons, is scrubbed out in amine scrubbers asClaus gas or hydrogen sulfide gas at concentrations of up to 90% byvolume of hydrogen sulfide. Hydrogen sulfide is also formed in the sourwater stripping columns. In this case, hydrogen sulfide is present asaqueous condensate and is stripped out as sour water stripper gas (SWSgas) containing up to 50% by volume of hydrogen sulfide. In addition, upto 50% by volume of ammonia (NH₃) can be present, which is formed bydecomposition of organic nitrogen compounds.

The combustion of coal or heavy oil in power stations in which the fuelis gasified in advance under an oxygen deficit also produces ahydrogen-sulfide-containing synthesis gas, which is purified prior tothe combustion.

Hydrogen sulfide, moreover, occurs at varying concentrations inassociated oil field gas and in natural gas at a content of up to 30% byvolume and in the off-gas from sewage treatment plants at a content ofup to 5% by volume of hydrogen sulfide.

The industrial utilization of hydrogen sulfide is limited. Therefore, itis first converted into elemental sulfur and then in special plants intosulfuric acid. Elemental sulfur is required in the rubber industry.Sulfuric acid is used in the chemical industry.

Direct conversion of sulfuric acid into elemental sulfur is possible bythermal cleavage of hydrogen sulfide, wet oxidation of hydrogen sulfidein a liquid (aqueous) phase and dry oxidation of hydrogen sulfide in thevapor phase.

The direct conversion process most frequently utilized with over 2000plants worldwide is the Claus process, which was developed as early as1883. This process is based on a dry oxidation process. A multiplicityof process variants have arisen. All process variants are based on thesame fundamental chemical reactions and on the use of a thermal reactorand a catalytic reactor.

The thermal reactor consists of a combustion chamber having a burner, awaste-heat boiler and a first sulfur condenser. The catalytic reactor isconstructed to have two or three stages. The stages each have a heater,a catalyst bed and a sulfur condenser.

In the combustion chamber and the catalytic reactors, the fundamentalchemical reactions below proceed: $\begin{matrix}\begin{matrix}\left. {{1.\quad \text{H}_{2}S} + {{1/2}O_{2}} + {1.88N_{2}}}\rightarrow{{{1/3}{SO}_{2}} + {{2/3}H_{2}S} + {{1/3}H_{2}O} + {1.88N_{2}}} \right. \\\left. {{2.\quad {1/3}{SO}_{2}} + {{2/3}H_{2}S} + {{1/3}H_{2}} + {1.88N_{2}}}\rightarrow{S + {H_{2}O} + {1.88N_{2}}} \right.\end{matrix} \\\left. {{\text{Overall:}H_{2}S} + {1.2O_{2}} + {1.88N_{2}}}\rightarrow{S + {H_{2}O} + {1.88N_{2}}} \right.\end{matrix}$

The remaining associated gases present due to the process, such ashydrogen, methane, higher hydrocarbons, ammonia, steam, carbon dioxide,react in accordance with their concentrations in a multiplicity of sidereactions.

The actual Claus reaction between sulfur dioxide and hydrogen sulfide inwhich elemental sulfur and steam are formed is reaction 2. This proceedsin the catalyst bed.

Elemental sulfur is additionally directly produced by the thermalcleavage of hydrogen sulfide into sulfur and water in the combustionchamber:

H₂S→H₂+½S₂

This reaction is highly endothermic.

In terms of the process, one third of the amount of hydrogen sulfide,usually a mixture of Claus gas and sour water stripper gas, is burnt bythe burner substoichiometrically by the combustion air to give one thirdof sulfur dioxide. The remaining hydrogen sulfide is thermally cleavedin the combustion chamber into sulfur and hydrogen in the temperaturerange between 900° C. and 1300° C. and is catalytically converted attemperatures between 180° C. and 400° C. in the catalytic reactorstogether with the unburnt hydrogen sulfide to give elemental sulfur andwater. The reaction to give sulfur is optimum when the hydrogensulfide/sulfur dioxide ratio is two to one. However, the optimum ratiois only reached to an approximation in practice.

The elemental sulfur formed in the combustion chamber is alreadyseparated off in the liquid state after cooling the process gasdownstream of the waste-heat boiler and in the first sulfur condenser.In the downstream catalytic reactors, the cooled process gas is heatedto the necessary reaction temperature prior to entry into the catalystsby the upstream heaters using high-pressure steam or a thermal oil. Thesulfur formed by the Claus reaction is likewise separated off in theliquid state in the sulfur condensers.

On account of the varying hydrogen sulfide concentration in the feedgas,in the conventional Claus processes, there are two main variants: themain stream operation for hydrogen sulfide concentrations above 50% byvolume and the side stream operation for hydrogen sulfide concentrationsbetween 30% by volume and 50% by volume.

In the main stream operation, the entire quantity of hydrogen sulfide ispartially combusted with the combustion air in the combustion chamber.Owing to the thermal cleavage of the hydrogen sulfide in the combustionchamber, a high proportion of sulfur is already separated off in thefirst sulfur condenser downstream of the waste-heat boiler. Forhydrogen-sulfide-rich gas, the degree of sulfur conversion in athree-stage Claus process is 96 to 97%.

Downstream tail gas treatment plants, generally Claus processes having athermal afterburning, then make it possible to comply with theregulatory limit values dependent on the plant capacity.

In the side stream operation, on account of the low heating value of thehydrogen sulfide gas, the gas stream is divided. At least one third ofthe hydrogen sulfide gas is burnt with the necessary combustion air inthe combustion chamber and the resulting sulfur-dioxide-rich reactiongas is mixed with the remaining hydrogen sulfide gas upstream of thefirst reactor. In this process, no elemental sulfur is formed in thecombustion chamber, since the hydrogen sulfide gas is completelycombusted.

At hydrogen sulfide concentrations below 30% by volume, even thesidestream operation is no longer usable, on account of the low heatingvalue. The combustion then becomes unstable. Furthermore, the sidestreamoperation generally requires an ammonia-free feedgas. Otherwise, thecatalysts are contaminated by ammonia via the bypass. When ammonia ispresent, for example when sour water stripper gas is used, the sourwater stripper gas must be burnt separately from the Claus gas in thecombustion chamber. These qualities of the feedgas require modifiedvariants of the Claus process.

The existing Claus plants frequently have an insufficient sulfurcapacity for a production-related increase in refinery capacity, use ofcheaper but higher-sulfur crude oil qualities or for reduced sulfurconcentration limit values in the end product. The term “sulfurcapacity” here means the amount of sulfur produced per unit time.

In addition to the new construction or conversion of the Claus plantwhich may be necessary, there is also the possibility of bypassing thebottleneck in the apparatus by the use of oxygen. In these processes,the combustion air is partly or completely replaced by oxygen. By usingoxygen, the combustion temperature is increased and the inert gascontent is decreased or eliminated. This means that specific process gasvolumes and thus the plant pressure drop are decreased. Thus thethroughput of the sour water gas and Claus gas can be increased andlow-hydrogen-sulfide feed gases having a low heating value and highammonia content can also be processed in a main stream reactor. The useof oxygen in Claus plants is currently the state of the art.

In the processes currently used, the enrichment of combustion air withoxygen is the easiest to implement. The increase in throughput hydrogensulfide is proportional to the rate of oxygen fed. The maximum possibleoxygen rate is limited by the permissible operating temperatures of theburner, the waste-heat boiler and of the first reactor.

Depending on the boiler present, the maximum permissible oxygenconcentration is 27 to 28% by volume, the permissible operatingtemperatures of the burner, the waste-heat boiler and the first reactorbeing limiting. The degree of conversion of sulfur is not increased incomparison with the conventional Claus process.

In the COPE process, the combustion air is enriched with oxygen,elevated concentrations at up to 100% by volume of oxygen being able tobe achieved. This requires a special burner and an additionalcirculation fan. In this process, the temperature increase in thecombustion chamber and in the waste-heat boiler due to the high oxygenconcentration is compensated for by recirculating cold process gas. Theprocess gas is drawn in downstream of the first sulfur condenser andblown into the combustion chamber through the burners to decrease thetemperature. The higher process gas rates increase the pressure drop inthe combustion chamber and in the waste-heat boiler. In the downstreamcatalytic reactor stages, the pressure drop is lower on account of thereduced process gas rates.

The Lurgi-oxygen-Claus burner is a burner which can be operated withair, with oxygen, or with air and oxygen as oxidation medium. Themaximum possible oxygen concentration is approximately 80% by volume.The Claus gas and the ammonia-containing sour water stripper gas are fedseparately. The sour water stripper gas is burnt together with the fuelgas with air in a central burner muffle. The Claus gas is burnt withoxygen and air as oxidation medium by a plurality of twin-concentricindividual burners which are symmetrically arranged around the burnermuffle. An individual burner consists of a central oxygen nozzle, aconcentric Claus gas nozzle and a twin-concentric air nozzle. Thisarrangement produces individual oxygen/hydrogen sulfide flames which aresurrounded by cold air/hydrogen sulfide flames. This controls thetemperature in the combustion chamber. Recirculation of cold process gasto decrease the temperature is not necessary even at high oxygen rates.

In the SURE process, oxygen-enriched air or 100% by volume oxygen islikewise used as oxidation medium.

In the SURE dual combustion process, combustion of the hydrogen sulfideis carried out by two combustion chambers which are connected in seriesand are each equipped with a waste-heat boiler and a sulfur condenser.The hydrogen sulfide gas is burnt with a portion of the oxygen in thefirst combustion chamber, cooled in a waste-heat boiler, transferred bya burner into the second combustion chamber and the amount of remainingoxygen required for the Claus reaction is added. This apportioninglikewise controls the temperature in the combustion chambers.

In the SURE sidestream burner process, a separate combustion chamber isconnected upstream of the existing Claus process. The hydrogen sulfidegas is apportioned between the two combustion chambers. In the firstcombustion chamber, combustion with oxygen produces sulfur dioxidealone. To control the temperature, downstream of the waste-heat boiler,a partial stream of the cooled sulfur-dioxide-containing partial streamis blown into the actual combustion chamber through a burner togetherwith the remaining hydrogen sulfide gas and oxygen in order to set thehydrogen sulfide/sulfur dioxide ratio necessary for the Claus reaction.

The use of up to 100% by volume oxygen as oxidation medium offers thegreatest potential for increasing the output of the Claus plants.However, for this purpose, not inconsiderable capital expenditure onplant equipment must be made. In all known oxygen-Claus processes, atleast the burners and the combustion chambers must be replaced. Furthercosts arise if, in addition, a recirculated gas fan or a secondcombustion chamber with waste-heat boiler and sulfur condenser arerequired. Furthermore, operating a recirculation fan is not withoutproblems owing to possible sulfur deposits.

However, the high potential operating capacity which is then availablecan usually not be exploited, since the downstream systems, thecatalytic reactors for example, are a bottleneck. In contrast, oxygenenrichment requires the lowest capital expenditure, but with only amaximum of 28% by volume of oxygen in the combustion air, it offers thelowest potential for increase in the efficiency of a Claus plant.

The object therefore underlying the invention was to overcome thedisadvantages of the prior art and to provide a process and an apparatusby which in particular the operating capacity and the degree ofconversion of hydrogen sulfide to elemental sulfur are improved. Theprocess and the apparatus, furthermore, are to be able to be integratedinto existing Claus plants with comparatively low additionalexpenditure.

The object is achieved by a process having the features according toclaim 1 and an apparatus having the features as described in claim 16.Preferred developments are specified in the subclaims.

The process according to the invention has the advantage that the sulfurcapacity of Claus plants is increased with the use of oxygen or anoxygen-rich gas, with only low capital costs being necessary. However,at the same time, substantially higher oxygen concentrations or hydrogensulfide throughputs are possible in comparison with a conventionaloxygen enrichment.

According to the invention, the oxygen is not used solely as oxidationmedium as hitherto, but is additionally used to increase the mixingenergy in order to improve the mixing between oxidizing agent andfeedgas in the existing combustion chamber. By increasing the mixingenergy, the combustion density and thus the throughput of hydrogensulfide can be increased. This is because this integrates, into theexisting combustion chamber, an additional afterburning zone which isproduced by highly turbulent self-priming oxygen jets. The process gaswhich is partially reacted with air or premixed and is exiting from thecombustor or the burner is thus subjected to complete afterburning.Furthermore, the reactions taking place in the combustion chamberproceed closer to the thermodynamic equilibrium. The terms “partialcombustion” and “afterburning” relate to the stoichiometric combustion.

Instead of technical-grade oxygen which is supplied compressed bypipeline or is taken off at high pressure in the liquid state fromvacuum-insulated containers, oxygen having a purity of 80% by volume to100% by volume oxygen content can also be used. This is preferablyproduced directly on-site by molecular sieve adsorption systems, forexample vacuum swing adsorption systems (VSA) or pressure vacuum swingadsorption systems (PVSA).

The additional oxygen is, according to the invention, not added ashitherto via the burner by enriching the combustion air, but ispreferably blown in at high velocity through at least one or amultiplicity of individual nozzles. These are, depending on the existingconstruction of the combustion chamber, installed symmetricallydistributed in the combustion chamber wall in the transition region tothe combustor or downstream of the burner at the beginning of thecombustion chamber.

The process gas which is exiting from the combustor or the burner and issubstoichiometrically burnt or premixed with the combustion air of theburner is, owing to the intensive mixing with the oxygen, subjected tocomplete afterburning and the stoichiometric hydrogen sulfide/sulfurdioxide ratio of two to one which is required for the Claus reaction isset, the hydrogen sulfide/sulfur dioxide ratio being measured upstreamof the tailgas treatment system.

For intensive mixing, the exit velocities from the individual oxygennozzles are preferably in a Mach number range between 0.4 and 2. Machnumber (Ma) is here taken to mean the ratio of the nozzle exit velocityto the speed of sound of the gases. On account of the relatively highexit velocity of the oxygen, highly turbulent free jets are formed whichdraw in surrounding combustion chamber atmosphere, mix and react withthe combustible constituents. The hydrogen sulfide in this case is burntto sulfur dioxide.

At an exit velocity corresponding to a Mach number of one, that is thespeed of sound, for example, on account of the intensive mixing, thestoichiometric hydrogen sulfide/sulfur dioxide ratio of two to one isestablished. This means, the oxygen present in the combustion chamber iscompletely reacted. The complete reaction of the oxygen increases theservice life of the first catalytic reactor. This is because at reactortemperatures of 380° C. to 550° C., the excess oxygen otherwise presentin Claus plants reacts with the sulfur dioxide present to form sulfurtrioxide (SO₃) which reacts with the aluminum oxide catalyst pelletsaccording to the following reaction equation:

Al₂O₃→Al₂SO₄+O₂

Aluminum sulfate forms, which coats the catalyst surface and thusinactivates the catalyst.

Furthermore, at oxygen velocities corresponding to a Mach number of 1,the oxygen nozzles are thermally relieved, since the flames of thehydrogen sulfide/sulfur dioxide free jet diffusion flames do notstabilize on the nozzle, but burn free in the combustion chamber, liftedoff from the nozzle. In addition, the flame routes are thus displacedfrom the oxygen nozzles into the combustion chamber. The absolute oxygenpressure at the nozzle exit necessary for an oxygen velocitycorresponding to a Mach number of 1 should preferably be 1.93 times thepressure prevailing in the combustion chamber (PBRK).

The angle of inclination of the oxygen injection lances is preferably45° to 90° to the direction of flow, the axes of the oxygen jetsintersecting the central axis of the combustion chambers. The oxygeninjection lances are advantageously installed into the inner wall of thecombustion chambers with the nozzles flush or recessed.

In the case of burners which produce swirling flames, that means whichhave a radial velocity and concentration distribution of the individualgas components on the combustion chamber, the oxygen injection lancesare preferably installed distributed symmetrically around the peripherypreferably at a distance of approximately 0.25 of the combustion chamberdiameter, measured from the center of the combustion chamber. Thisproduces an oxygen swirled flow directed against the swirl of the mainflame.

The oxygen injection lances are preferably concentric, the oxygen nozzlebeing surrounded by a ring-gap nozzle. A protective gas having a minimumexit velocity corresponding to a Mach number of 0.2 is advantageouslypermanently blown into the combustion chamber through the ring-gapnozzle, in order to cool the oxygen nozzle and to protect against sulfurdiffusing in.

The protecting gas used is preferably air, nitrogen or carbon dioxide.

Experiments have shown that, using this process, depending on thehydrogen sulfide concentration, equivalent oxygen concentrations (XO₂)of 21% by volume to 40% by volume of oxygen can be achieved. Theequivalent oxygen concentration is described here by the equation

(XO₂)=0 ₂ total/(air+O₂ additional).

The rates of Claus gas and sour water stripper gas are increased inaccordance with the oxygen supply.

EXAMPLES

The examples below show that the temperature in the combustion chamberincreases on account of the high equivalent oxygen concentration andcombustion density. More steam is produced in the waste-heat boiler onaccount of the higher amount of waste heat (see table).

Example Example Example 1 2 3 Claus gas kg/h 442 603 706 SWS gas kg/h240 259 246 Air, total kg/h 1515 1222 797 Oxygen kg/h 0 71 146Combustion chamber temp. ° C. 1213 1331 1415 Waste-heat boiler temp. °C. 597 617 641 Burner temperature ° C. 297 259 268 Reactor temp. R1 ° C.355 387 395 H₂S/SO₂ ratio 2.08 2.01 2.01 Sulfur capacity % 100 126 142X_(Claus-gas) = 85% by volume, X_(SWS-gas) = 46% by volume

In the event of an increase of the permissible combustion chambertemperature of 1500° C., the equivalent oxygen concentration can beincreased to at least 40% by volume. Since heat and mass are exchangedequally rapidly, the temperature in the combustion chamber is evened outat a higher level as a result of the intensive mixing and the heattransfer to the combustion chamber wall is improved. This means that theamount of heat released to the surroundings via the combustion chamberwall is greater. The waste-heat boiler is thermally relieved. Thetemperatures at the burner and in the combustor do not increase.

The process causes the temperatures to increase due to the higher sulfurconversion in the catalytic reactor, with the permissible operatingtemperature of the catalyst of up to 650° C. being able to be exploited.The high combustion temperatures when oxygen is used have beneficialeffect on the thermal cleavage and complete combustion of higherhydrocarbons and ammonia, in which case, in particular, a minimumtemperature of 1350° C. should be maintained for complete cleavage andcombustion of ammonia. Owing to the lack of nitrogen ballast, at anequivalent oxygen concentration of 40% by volume, the concentration ofhydrogen sulfide gas in the gas mixture used can be decreased to 20% byvolume of hydrogen sulfide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section of a combustion chamber to which are connected alance for introducing oxygen into the combustion chamber and a burnercomprising a combustor according to a first embodiment of the invention;

FIG. 2 shows a section of a combustion chamber to which are connected alance for introducing oxygen into the combustion chamber and a burnercomprising a combustor according to a second embodiment of theinvention; and

FIG. 3 shows a section of a combustion chamber to which are connected alance for introducing oxygen into the combustion chamber and a burneraccording to a third embodiment of the invention.

FIGS. 1 to 3 show a burner and the section connected thereto of thecombustion chamber or combustion chamber of a Claus plant, the burnershown in FIG. 1 and FIG. 2 additionally having a combustor.

FIG. 1 shows the burner (1) to which are fed via a 3-fold concentrictube (2) having an inner pilot tube (3) a fuel gas via the middle tube(4) and the Claus/SWS gas via the outer tube (5). Air is passed into theburner (1) via line (6). The combustion takes place in the combustor (7)and combustion chamber (8) connected thereto. According to theinvention, oxygen is introduced at high velocity into the combustionchamber via a nozzle (9). In addition, it is shown here that the lancefor introducing the oxygen (10) consists in its front region of atwin-concentric tube, the oxygen being introduced by the inner tube (11)and a protecting gas to cool the nozzle (9) being introduced via theouter tube (12). The angle “β” here denotes the angle of inclination ofthe oxygen lance in relation to the direction of flow (R). The angle “β”according to the invention is in the range from 45° (β) and 90° (β′).Combustor (7) and combustion chamber (8) are here a one-piececonstruction.

FIG. 2 shows a similar embodiment as FIG. 1, combustor (7) andcombustion chamber (8) being separate from one another. The burner (1)has a three-fold concentric tube (2) having an inner tube (3) for pilotgas, a middle tube (4) for fuel gas and an outer tube (5) for Claus/SWSgas. Air is fed via a line (6). A combustor (7) is arranged upstream ofthe combustion chamber (8). Oxygen and a protecting gas are fed via atwin-concentric tube, the oxygen being conducted in the inner tube (11)and the protecting gas in the outer tube (12). The oxygen lance is at anangle β to β′ (45° to 90°) to the direction of flow (R).

In FIG. 3, the combustion chamber (8) is directly connected to theburner (1) of the Claus plant. In this embodiment, the pilot gas isintroduced into the burner via a separate tube (13).

What is claimed is:
 1. In a process for producing elemental sulfur bycombustion of hydrogen sulfide or a hydrogen sulfide-containing gas in acombustion whereby the hydrogen sulfide or the hydrogensulfide-containing gas is treated by partially combusting with additionof air as the oxidation medium, subjecting the partially combustedhydrogen sulfide or hydrogen sulfide-containing gas to afterburning byadding an oxygen-containing gas to the partially combusted gas, andfeeding the reaction gas mixture to a waste-heat boiler and thereafterto one or more catalytic reactors, characterized in that an afterburningzone is intergrated into the combustion reactor located downstream andseparate from a burner by feeding the oxygen-containing gas directlyinto the combustion reactor by a multiplicity of individual nozzles, andfeeding the oxygen-containing gas into the combustion reactor at anintake velocity in the range between Mach number 0.4 and
 2. 2. Theprocess as claimed in claim 1, in which the oxygen-containing gas has aconcentration of 80% by volume to 100% by volume of oxygen.
 3. Theprocess as claimed in one of claim 1, in which the intake velocity ofthe oxygen-containing gas into the combustion reactor is in the range ofa Mach number between 0.4 and 2, as a result of which the mixing betweenthe oxygen containing gas, the combustion air and thehydrogen-sulfide-containing process gas is increased.
 4. The process asclaimed in claim 1, in which the air combusts the fuel in the burner toform a flame which enters into the combustion reactor in a flowingdirection and the oxygen-containing gas enters into the combustionreactor at an angle of 45° to 90° inpinged against said flowingdirection.
 5. The process as claimed in claim 4, in which, in the caseof a process having swirl of the main flame in the combustion reactor, aswirl flow of the oxygen-containing gas is produced which impingesagainst the swirl of the main flame.
 6. The process as claimed in claim1, in which the entry point of the oxygen-containing gas into thecombustion chamber is cooled and is protected against sulfur diffusingin.
 7. The process as claimed in claim 6, in which, for cooling andprotecting, a protecting gas is fed to the combustion reactor in theregion of the point of entry of the oxygen-containing gas into thecombustion reactor.
 8. The process as claimed in claim 6, in which air,nitrogen or carbon dioxide is used as the protecting gas.
 9. The processas claimed in claim 7, in which the intake velocity of the protectivegas into the combustion chamber is at least Mach number 0.2, as a resultof which the turbulent mixture between the oxygen containing gas, thecombustion air and the hydrogen-sulfide-containing process gas isadditionally increased.
 10. The process as claimed in claim 1, in whichthe rate of oxygen fed is controlled in accordance with thestoichiometry of a Claus reaction in such a manner that the oxygen andthe combustion air react completely with hydrogen sulfide and the othercombustible gases so that no excess oxygen is present downstream of thecombustion chamber.
 11. The process as claimed in claim 1, in which therate of oxygen fed is controlled in accordance with the stoichiometry ofa Claus reaction in such a manner that the maximum temperatures in theburner is 2500 C. and that the maximum temperature in the combustor is12000 C. and the maximum temperature in the combustion reactor is 15000C., so that the heat transfer to the combustion reactor wall isminimized and the maximum temperature in the waste-heat boiler is 6700C.
 12. The process as claimed in claim 1, in which the concentration ofoxygen in the oxygen-containing gas (equivalent oxygen concentration) isbetween 21 and 40% by volume.
 13. The process as claimed in claim 1, inwhich the concentration of the hydrogen sulfide in the feed gas is atleast 20% by volume.
 14. An apparatus for producing elemental sulfur bycombustion of hydrogen sulfide or a hydrogen sulfide-containing gas,comprising a combustion reactor to which a burner is fixed in which thehydrogen sulfide or the hydrogen sulfide-containing gas is partiallycombusted with addition of air, a waste-heat boiler and one or morecatalytic reactors, characterized in that a multiplicity of nozzles aredirectly fixed to the combustion reactor downstream from the burner,through which an oxygen-containing gas is fed into the combustionreactor, as a result of which the hydrogen sulfide or the hydrogensulfide-containing gas is subjected to afterburning.
 15. An apparatus asclaimed in claim 14, in which the nozzles, in the installed state, arearranged flush or recessed in the refractory brick lining of thecombustion reactor.
 16. The apparatus as claimed in claim 14, in whichin the case of a process having a swirled main flame in the combustionreactor the nozzle is installed tangentially at a distance from thecenter of the combustion reactor which corresponds to 0.25 times thediameter of the combustion reactor, so that a swirl flow of the oxygenor oxygen-containing gas is produced which is impingesd against theswirl of the main flame.
 17. The apparatus as claimed in claim 14, inwhich a ring-gap nozzle is arranged around the nozzles for blowing inthe oxygen or the oxygen-containing gas, through which ring-gap nozzle aprotective gas is additionally blown in.
 18. The apparatus as claimed inclaim 14, in which the multiplicity of nozzles are symmetricallyinstalled in the combustion reactor wall.